Genus: Unicellular; variable in shape; a constriction at the center of the cell body; mostly longer than wide; flattened; each semicell hemispherical, spherical, ellipsoidal, rectangular, pyramidal or kidney-shaped; no apical indentation
Subgenus [Eucosmarium]: Cell body dorso-ventrally compressed, with strong constriction at the center, transverse section elliptical or diamond-shaped.
Section [Margaritiferae]: Cell surface granulated, gnarled or spiny; semicells pyramidal with flattened apex or trapezoid (Illustrations of The Japanese Fresh-water Algae, 1977).
Species[ punctulatum ]: Cell body 34-41 μm long, 31-35 μm wide, isthmus 8-10 μm wide; (Illustrations of The Japanese Fresh-water Algae, 1977).

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C. punctulatum var. punctulatum 37 x 32 μm water reservoir near Yamaguchi Univ. Yamaguchi, 2004	C. punctulatum v. punctulatum 36 x 32 μm Numa-no-hara m. Madarao highland Niigata, 2005	C. punctulatum var. punctulatum 35.5 x 32.5 μm Numa-no-hara m. Madarao highland Niigata, 2006	C. punctulatum var. punctulatum ? 34 x 30 μm Okubo Ryoke Akigase park Saitama, 2005.2
C. punctulatum v. punctulatum 31 x 29 μm Okubo Ryoke Akigase park Saitama, 2005.4	C. punctulatum var. rotundatum 38-45 x 32-35 μm Maimeno-ike Norikura highland Nagano, 2006	C. punctulatum var. rotundatum 36 x 30 μm Ichinose-enchi Norikura highland Nagano, 2006
C. punctulatum v. subpunctulatum or C. orthostichum ?? 30 x 27 μm Higashi-sano Hakuba Nagano, 2004	C. punctulatum var. punctulatum or C. orthostichum ?? 30 x 26 μm Shimo-muneoka Shiki Saitama, 2004	C. punctulatum var. punctulatum or C. orthostichum ?? 28 x 16 μm Univ. A.V.M. Obihiro Hokkaido, 2005

Similar species -- >> C. orthostichum; C. subtumidum (Pyramidatae);

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